1. Field of the Invention
The present invention is related to the field of delivery devices and, more particularly, to a method of producing rapidly dissolving pharmaceutical tablets.
2. Description of the Related Art
Many people, particularly the young and the elderly, have difficulty swallowing orally administered medications. These difficulties may arise from an inability to chew and/or swallow pills and tablets. Tablets that disintegrate rapidly, and preferably without water, are therefore highly desirable.
To achieve rapid dissolution, tablets need to be sufficiently porous. However, the tablet must also maintain its integrity prior to administration. Therefore, a need exists for a rapidly disintegrating tablet having enhanced structural integrity.
U.S. Pat. No. 4,134,943 describes a process for developing a fast dissolving tablet that requires a solvent that is inert to all components of the tablet. After mixing of all the components in the solvent, the mixture is frozen and pressed into a tablet. The solvent is then evaporated to form the porous tablet. The process is complex and quite expensive.
Another freeze drying process for forming porous tablets is described in U.S. Pat. No. 4,371,516. A gelatin or other water-soluble binder along with the pharmaceutical and acceptable sugars are all dissolved and the mixture placed in a suitable mold. The mixture is frozen and the solvent removed under vacuum. The tablets are expensive to prepare and require special packaging due to their lack of strength.
U.S. Pat. No. 5,516,530 describes an even more complex system for forming porous tablets using lyophilization. U.S. Pat. No. 5,298,261 describes a freezing process followed by vacuum drying that makes for a less porous tablet than is seen in the prior lyophilization processes.
U.S. Pat. No. 3,885,026 describes the incorporation of a readily volatilizable solid excipient into a tablet, producing a porous yet strong shape after sublimation. Dissolving times are listed at 105 to 270 seconds, which is too long for the purposes to which the present invention is directed.
A further weakness in the prior art methodologies relates to the dissolution or suspension of all components in water. When excipients as well as the active ingredients are dissolved, this precludes the use of controlled release or coated active ingredients for taste masking. More particularly, during preparation of the aqueous suspension prior to freeze drying, the coated particles can release a sufficient amount of the active ingredients to render the final tablet, after drying, unpalatable. Accordingly, a need exists for a methodology in which all dry ingredients can be used, without the need for water, so as to maintain taste masking while yet creating the requisite tablet porosity for fast dissolution.
In view of the foregoing, one object of the present invention is to overcome the difficulties that some patients encounter with orally administered medications through the production of a tablet that dissolves quickly in the mouth, allowing for effortless swallowing without any need for drinking water.
Another object of the invention is to produce a fast-dissolving tablet by optimizing component particle size ranges to promote both optimum release and tablet strength.
A further object of the invention is to produce a tablet having sufficient strength by controlling the amount of excipient within specified ranges.
A still further object of the invention is a tablet that does not require suspension of all components in water during formation and therefore allows for effective taste masking of the active ingredient.
Yet a further object of the invention is a tableting process that is cost effective, requiring only commercially available raw materials and standard tablet dies and associated machinery.
In accordance with this and other objects, the present invention is directed to a method of producing a fast-dissolving pharmaceutical delivery device of moderate strength. The formulation employed in the method utilizes at least one carbohydrate, a strengthening polymer, a volatile pore-forming excipient, and a physiologically active ingredient. By controlling and optimizing the particle size distribution ranges of the components prior to tablet formulation, particularly of the pore forming excipient, a much faster releasing tablet is obtained.
These and other objects of the invention, as well as many of the intended advantages thereof, will become more readily apparent when reference is made to the following description taken in conjunction with the accompanying examples.
In describing a preferred embodiment of the invention, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.
According to the present invention, the method of formulation utilizes one or more carbohydrates, a polymer for improving tablet strength, a volatile excipient such as ammonium bicarbonate, along with taste masking flavorings and a physiologically active ingredient. The carbohydrates may be one or more of the following examples: lactose, mannitol, sorbitol, fructose or other highly water-soluble sugar or sugar alcohol.
Particle sizes and the nature of the carbohydrate can affect both the strength and the taste of the final tablet. Lactose and sorbitol combinations are the most favorable for improving the rate of dissolution, with sorbitol concentration at approximately 10 to 35% of the pre-processed tablet mass and more specifically, 15 to 20%. Lactose concentration at 15 to 50% also proved effective, with the optimum being 30% to 40% of the pre-processed mass. Processing as defined herein is the removal by sublimation of the volatile tablet component.
Sorbitol is employed for its pleasing taste-modifying properties while the lactose is used for its superior dissolution property. Mannitol can be substituted for the lactose with only a slight decrease in disintegration time. Small amounts of maltodextrin improve the tablet strength but with the sacrifice of release time.
Sugar particle size is optimized to improve the strength and the dissolution times, with a particle size below 75 microns being desirable and, more specifically, 37 to 70 microns being optimal.
A volatile excipient such as ammonium carbonate or ammonium bicarbonate is known to create porosity in the tablet after it is heated under a vacuum for several hours. However, according to the present invention, the disintegration times of the final tablets are markedly reduced if finely ground ammonium carbonate is used. More particularly, the disintegration times as measured in a rotating basket submerged in water are greatly reduced when all of the particles of ammonium carbonate are below 70 microns in size, and preferably in the range of 37 to 70 microns. The use of even finer particles of carbonate produced only slight improvement in disintegration times.
Ammonium carbonate and ammonium bicarbonate may be used somewhat interchangeably in accordance with the present invention. Therefore, references herein to ammonium carbonate shall be understood to include the use of ammonium bicarbonate in place thereof, and vice versa. However, in practice it is noted that carbonate is preferred since water is not present during decomposition.
Controlling particle size in accordance with these ranges not only decreases the release time but increases the ultimate tablet strength. The tablet appearance is also considerably improved since there are no large pores evident on the tablet surface as occur with the use of larger particles of bicarbonate.
The smaller ammonium bicarbonate particles produce somewhat weaker tablets. Tablets made with ammonium bicarbonate sieved below 38 microns were approximately 40% weaker than those containing ammonium bicarbonate sieved below 100 microns (average size of about 60 microns). However, this reduction in strength was ameliorated, without greatly sacrificing the disintegration time, by employing ammonium bicarbonate sieved below 53 microns.
The amount of bicarbonate used in forming a tablet (pre-processed mass) also has a profound effect on disintegration, more so than its effect on tablet strength. For example, a half-inch diameter tablet with a pre-processed mass of 500 mg pressed at the same pressure showed a 40% slower release at 25% ammonium bicarbonate than a tablet containing 35% bicarbonate with the other ingredients in equal ratios. The difference in strength between the two tablets was minimal, with the 25% tablet being slightly stronger. Therefore, within a narrow range of concentration, the bicarbonate content can be increased to improve disintegration without unduly sacrificing tablet strength.
Small amounts of microcrystalline cellulose, starch, or maltodextrin can improve the strength of the tablets without significant increase in disintegration times. Particle size for these excipients was of less importance with regard to impact on the disintegration times. Approximately 2% to 8% of each of microcrystalline cellulose (for example, Avicell(copyright) of FMC) and starch (as Starch 1500, Colorcon, e.g.), more specifically 5% each, gave improved tablet strength. Small amounts of polyvinyl pyrolidone (ISP K-30), up to approximately 3%, gave improved strength without greatly affecting release times. The addition of mannitol also gave improved strength to the tablets without greatly sacrificing the dissolution behavior.
The following examples are given for the purpose of illustrating the present invention. The tablet dissolution performance was measured using a rotating basket procedure. Release times were measured by placing the tablet in a small wire basket placed on the end of a rod spinning at 100 rpm. This was placed in water and the dissolution time was noted when the tablet was completely disintegrated and there were no pieces retained by the basket screen.